This invention relates to communication systems. More particularly, and not by way of limitation, the invention is directed to a system and method of supporting packet-switched handover.
Provisions for packet-switched (PS) handover are included in 3rd Generation Partnership Project (3GPP)/GERAN specifications. These provisions allow for PS handover between GPRS/EDGE radio access network (GERAN) and UMTS terrestrial radio access network (UTRAN) cells. PS handover principles are defined in 3GPP TS 43.129 in 3GPP Release-6.
A 3GPP work item, “Evolved UTRA and UTRAN” (E-UTRA and E-UTRAN respectively), defines Long-Term Evolution (LTE), designed to improve efficiency, lower costs and improve services for 3GPP-based access technology. LTE will use Orthogonal Frequency-Division Multiplexing (OFDM) radio technology in the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink, allowing at least 100 Mbps peak data rate for downlink data rate and 50 Mbps for uplink data rate. LTE radio can operate in different frequency bands and is therefore very flexible for deployment in different regions of the world, where different frequency bands might be licensed.
In addition to the Radio Access Network (RAN) standardization, a 3GPP System Architecture Evolution (SAE) work item is being worked on to develop an evolved core network (CN) for LTE networks. The SAE core network is made up of core nodes, which may be further split into Control Plane (Mobility Management Entity, MME) nodes and User Plane Gateway (Serving Gateway and Packet Data Network (PDN) Gateway) nodes. In this application, the term Access Gateway (AGW) is used to depict both the Serving Gateway and the PDN Gateway nodes and functions. In the terminology currently used, AGW contains both User Plane Entity (UPE) and Inter-Access Anchor (IASA) functionality. The MME is connected to an E-UTRAN NodeB (eNodeB) via a S1-MME interface, and the AGW (i.e. the Serving Gateway) is connected to an eNodeB via an S1-U interface.
Currently, PS handover procedures allow for minimal service interruptions at network-controlled cell change by utilizing the principle of make-before-break meaning that the radio resources in the target cell are allocated before the mobile station (MS) moves to the target cell. In addition, the Location Area Updating (LAU) and Routing Area Updating (RAU) procedures as defined in 3GPP TS 24.008 are performed in parallel with the flow of user plane PS data during the PS handover execution phase to help minimize the interruption to user plane PS data flow experienced during PS handover.
However, currently there are no provisions for PS handover between a GERAN/UTRAN and a Generic Access Network (GAN) cell, between a GERAN and an Enhanced-UTRAN (i.e., LTE) cell, or between a LTE and a GAN cell. Specifically, there are no systems or methods for allowing PS handover between GERAN and GAN cells or between UTRAN and GAN cells or between LTE and GAN cells. Generic Access to the A and Gb interfaces is defined in 3GPP TSs 43.318 and 44.318. Vocabulary for 3GPP specifications is also defined in 3GPP TS 21.905 and is also utilized in the following description.
Without the capability of a PS handover procedure during a cell change to or from a GAN cell, service interruptions are increased and are determined by the time required to first complete the LAU and RAU procedures in the new cell (or relevant other similar procedures for LTE and SAE, for example Tracking Area Updates (TAU)) as well as by the time required to establish the necessary radio resources in the new cell. In the case where the MS also changes SGSN when performing cell change to or from a GAN cell, performing the RAU procedure means that the relevant information for the MS is retrieved from the previous (source) SGSN and forwarded to the new current (i.e., target) SGSN, which further increases the service interruption time. In addition, radio resource establishment time is an issue when a mobile station (MS) moves into a GERAN cell, given the nature of temporary block flow (TBF) establishment procedures.
Additionally, without a PS handover procedure for use during cell change to and from GAN cells, TBFs in a GERAN cell (and Radio Access Bearers (RABs) in a UTRAN cell) would need to be dropped prior to GAN rove-in (where rove-in implies a cell change procedure performed without using the PS handover procedure). The equivalent GAN radio resource, Generic Access-Packet-Switched Resources (GA-PSR) Transport Channel (GA-PSR TC), would then also need to be established after the rove-in, both of which (i.e. dropping of radio resources in the GERAN/UTRAN and allocating radio resources in the GAN cell) would add to the service interruption experienced by active PS services. If voice over IP (VoIP) is supported on one of the TBFs/RABs prior to cell change, then releasing the TBF/RAB prior to rove-in forces Session Initiated Protocol (SIP) signaling to be once again invoked in order to set up the VoIP session after rove-in to the new cell, thereby causing a corresponding delay.
A system and method of supporting PS handover between a GERAN or UTRAN cell or LTE cell and a GAN cell is needed to allow packet data transfer to occur while LAU and RAU procedures are ongoing and to avoid incurring delays in performing SIP signaling after cell change. This is particularly important since GERAN specifications are moving toward fully supporting VoIP service (e.g., with the specification of reduced transmission times and fast acknowledgement/no acknowledgement reporting as part of the Latency Reduction work effort) which makes avoidance of additional SIP signaling in the new cell (i.e. prior to PS service resumption) even more important.
Thus, it would be advantageous to have a system and method of supporting PS handover between GERAN or UTRAN cells and GAN cells. The present invention provides such a system and method.